This invention relates to a corrosion resistant copper-nickel alloy particularly suited for use in dairy equipment and other food industries.
Copper-nickel alloys, popularly known as "Nickel Silvers" and "Dairy Metals" typically contain up to 5 weight percentage lead. For decades they have been used in contact with many dairy products, meat and poultry, juices, and other comestibles etc. During the past two decades it has been established that lead causes severe health problems in human beings even when present as only a few parts per billion in food. As a consequence, there is a concentrated effort to eliminate lead in metals that will be in contact with food. Lead was incorporated in dairy metals to give lubricating quality which reduces friction in metal to metal rubbing contact. Various foreign and domestic equipment certifying agencies have already declared that they will not accept any lead bearing materials in contact with food.
In the present invention a copper base alloy is disclosed which has all the desirable properties of dairy metals but contains no lead. The new alloy has acceptable mechanical properties, is readily cast, is easily machined and has good bearing qualities in that it moves freely upon itself or stainless steel without galling.
Prior approaches to materials for corrosion-wear-sanitary conditions have focused on nickel-base alloys of Thomas and Williams U.S. Pat. No. 2,743,176 and Larson U.S. Pat. No. 4,702,887. The present alloy is substantially less expensive compared to these nickel-base alloys. Additionally, the present alloy has the following features which are superior to nickel-base alloys.
1. Present alloy has better castability in the sense that it is less prone to micro-shrinkage than nickel-base alloys. PA0 2. Present alloy is less prone to hot tearing than nickel-base alloys of U.S. Pat. Nos. 2,743,176 and 4,702,887. As a result complex shape parts may be cast out of present alloy, but they are not possible in alloys covered by the above patents. It is worth mentioning here that none of these alloys is amenable to weld repair. PA0 3. Present alloy is less prone to hydrogen gas pick-up than nickel-base alloys. Hydrogen pick-up may result in gas porosity in cast parts. PA0 4. Present alloy has much better machinability than nickel-base alloys.